[Trilinos-Users] ilut setting

[Chris Jackson]

I don’t know if this applies to the one you are talking about, but I recall that with one of the ILUT preconditioners the fill value is expected to be between 0.0 and 1.0.  1.0 meant essentially we were finding the inverse of the matrix.  Before we figured that out we were always astounded that BiCGStab was converging in 2 iterations…

Chris Jackson


From: trilinos-users-bounces at software.sandia.gov [mailto:trilinos-users-bounces at software.sandia.gov] On Behalf Of Hoang Giang Bui
Sent: Tuesday, September 17, 2013 6:28 PM
To: Erik Boman
Cc: trilinos-users at software.sandia.gov
Subject: Re: [Trilinos-Users] ilut setting

Hi Erik
I tried to increase "fact: ilut level-of-fill" to 50.0 and it still doesn't converge. In fact, with this value the preconditioner take very long to compute. Is there other option we can set for Ifpack ILUT?
Giang Bui

On Tue, Sep 17, 2013 at 8:01 PM, Erik Boman <egboman at sandia.gov<mailto:egboman at sandia.gov>> wrote:
Giang Bui,

You will not get exactly the same answer because the ILUT implementations are different in AztecOO and Ifpack. Also, the meaning of "fill" may be slightly different. Try increase the value of  "fact: ilut level-of-fill" in the Ifpack parameter to see if you can make it converge.

Erik

Hoang Giang Bui wrote:
Dear Trilinos developers,

Is there difference between 2 settings:

solver_parameters.set("AZ_solver", "AZ_bicgstab")
solver_parameters.set("AZ_kspace", 1000)
solver_parameters.set("AZ_output", 100)
solver_parameters.set("AZ_precond", "AZ_dom_decomp")
solver_parameters.set("AZ_subdomain_solve", "AZ_ilut")
solver_parameters.set("AZ_drop", 0.0)
solver_parameters.set("AZ_ilut_fill", 10.0)
aztec_solver.SetParameters(solver_parameter, true);

And:
solver_parameters.set("AZ_solver", "AZ_bicgstab")
solver_parameters.set("AZ_kspace", 1000)
solver_parameters.set("AZ_output", 100)
solver_parameters.set("AZ_precond", "AZ_none")
aztec_solver.SetParameters(solver_parameter, true);
IFPreconditionerType = "ILUT"
preconditioner_parameters.set("fact: ilut level-of-fill", 10.0);
preconditioner_parameters.set("fact: drop tolerance", 0.0);
overlap_level = 1
mPrec = Teuchos::rcp(Factory.Create(IFPreconditionerType, &rA, overlap_level));
mPrec->SetParameters(preconditioner_parameters);
aztec_solver.SetPrecOperator(&*(mpPrec->GetOperator()))

I thought it all resulted in Additive-Schwartz preconditioner with ILUT as local subdomain preconditioner. But it gives different performance. The first setting works well but the second failed to converge.

Best regards
Giang Bui
_______________________________________________
Trilinos-Users mailing list
Trilinos-Users at software.sandia.gov<mailto:Trilinos-Users at software.sandia.gov>
http://software.sandia.gov/mailman/listinfo/trilinos-users





--
With Best Regards !
Giang Bui
To learn and to excel
-------------- next part --------------
An HTML attachment was scrubbed...
URL: https://software.sandia.gov/pipermail/trilinos-users/attachments/20130918/8dabc176/attachment.html